Question

A current transformer has a phase error of +3°. The phase angle between the primary and secondary currents is
1. 3° 
2. 177° 
3. 180° 
4. 183° 

Answer 1

Correct Answer - Option 2 : 177° 

Phase angle error:

• Phase angle(δ) of the current transformer is the angle between the primary current I_p and secondary current I_s when reversed.
• The primary and secondary phasor difference is to be 180° in the case of an ideal current transformer.
• But in practice, this angle having a difference of θ is called phase angle error.
• So, for practical current transformer θ + δ = 180°.
• The total primary current is not actually transformed in the current transformer. One part of the primary current is consumed for core excitation and the remaining is actually transformers with a turns ratio of the current transformer.
• Both ratio error and phase angle error are due to the excitation current I_e.
• Especially, the ratio error is due to the iron loss component I_w and phase angle error is due to magnetizing component I_m.

 

Calculation:

Given that

Phase angle error θ = 3°

Phase angle between the primary current I_P and secondary current I_S = δ = 180° - θ = 180° - 3° = 177°